Page 57 - BSAVA Guide to Pain Management in Small Animal Practice

BSAVA Guide to Pain Management in Small Animal Practice

VetBooks.ir fewer side e ects than other opioids although it intravenous bolus or infusion (its short duration
can cause dysphoria in dogs. It frequently
of action limits its usefulness by the
intramuscular route). Fentanyl transdermal
causes euphoria in cats, and can be used to
improve cooperation in some feline patients. patches (unlicensed) have been used in both
Buprenorphine has a bell shaped dose dogs and cats, and can provide analgesia for
response curve in some species (in theory it several days.
could antagoni e its own e ect at higher doses , The injectable solution can be used in both
so practitioners are often reluctant to use it to dogs and cats as a co-induction agent and to
e ect. owever, the plateau of the curve occurs provide intra- and postoperative analgesia.
at doses much higher than those used clinically nset of action is less than minutes when
. mg kg in rats, um and er , 1981 . administered as a bolus, making fentanyl very
Therefore, the bell-shaped curve is not clinically useful for providing analgesia in response to
relevant and supplemental doses can be given surgical stimulation intraoperatively. If surgical
(and are licensed). stimulation is sustained, an intravenous infusion
Buprenorphine can be used to partially can be administered, and the dose rate titrated
antagoni e the e ects of a full P agonist. or to e ect; additional boluses can be given as
example, if a patient is dysphoric or over- necessary. Concerns about accumulation of
sedated following the administration of a MOP fentanyl during infusion seem to be unfounded
agonist, buprenorphine can be administered to based on a study that assessed the
reduce these unwanted e ects while still pharmacokinetics of a 1 g kg intravenous
providing some analgesia. This is called bolus followed by an infusion of 1 g kg hour
sequential analgesia and has been for up to 4 hours Sano et al., 6 . uring
demonstrated in humans and in rabbits sedated general anaesthesia, administration of a
with fentanyl uanisone lecknell et al., 1989 . fentanyl bolus or infusion can cause
bradycardia, respiratory depression or even
Fentanyl: Fentanyl is a full MOP agonist with a apnoea. It is advisable to discontinue fentanyl
rapid onset and short duration of action at the infusion at least minutes before the end of
doses commonly used clinically. The doses anaesthesia to avoid respiratory depression in
recommended in igure . are lower than the the recovery period. Respiratory depression is
licensed doses, but the authors have found very unlikely to occur in conscious patients.
them to be e ective. It is highly lipid soluble, Fentanyl patches have been widely used to
and resolution of its e ects may be due to provide long-term analgesia in dogs and cats
redistribution rather than metabolism. At higher although they are unlicensed. An area of
doses it may accumulate. It is currently licensed relatively immobile skin, for example, at the
for dogs as a g ml in ectable solution for dorsal or lateral thorax should be clipped and

Use of full MOP agonists following buprenorphine administration
f an appropriate dose of uprenorphine does not achieve the re uired analgesic effect, a full
MOP agonist can be administered. It is still not clear if adjustment of the dose of the full agonist
is required, and if so, whether an increase or decrease of the dose is appropriate. Whatever
course of action is chosen, it is unlikely to harm the patient. Trial therapy with the usual dose of
the full MOP agonist seems sensible; supplemental doses can be administered if necessary.
Alternatively, the full MOP agonist could be administered in small intravenous increments until
analgesia is achieved. In this situation it is also important to use multimodal analgesia as some
types of pain may respond better to other classes of analgesics than to opioids. If use of a full
MOP agonist for intraoperative analgesia is anticipated, for example, epidural morphine injection
or fentanyl infusion, it makes sense to use a full MOP agonist in the pre-anaesthetic medication
rather than buprenorphine.

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